Photoreaction and Active Oxygen Generation by Photosensitization of a New Antibacterial Fluoroquinolone Derivative, Orbifloxacin, in the Presence of Chloride Ion.

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The photoreaction of orbifloxacin (ORFX), a fluoroquinolone derivative having a fluorine at the 8 position, was investigated in aqueous solution containing chloride ion to determine its photochemical properties. In the presence of chloride ion, ORFX was found to convert into a photoproduct substituted by chlorine at the 8 position (8-Cl ORFX) under irradiation by ultraviolet-A (UVA) light. Although the formation rate of 8-Cl ORFX increased greatly with increase in chloride ion concentration, the apparent photodegradation rate of ORFX in aqueous solution was not varied by the presence of the ion. This implies that the dissociation of the C-F bond at the 8 position is the rate-limiting steps in the photodegradation of ORFX. The active oxygen generated by the photosensitization of ORFX were determined by measuring the bleaching rate of p-nitrosodimethylaniline and the reduction rate of cytochrome c. Their generation was inhibited by sodium azide and superoxide dismutase but not by D-mannitol.The photoreaction between ORFX and chloride ion also inhibited their generation. The mechanism is believed to be the photochlorination at the 8 position competing with the reaction between free radical and oxygen.